Unireturn flow steam cylinder



April 3, 1934. F. w. DEAN 1,953,674

UNIRETURN FLOW STEAM CYLINDER Filed NOV. 1, 1930 3 Sheets-Sheet l I @veniov: Franz mas Wfiean,

by T/MML fliiys.

April 3, 1934. F. w. DEAN UNIRETURN FLOW STEAM CYLINDER Filed Nov. 1, 1930 3 Sheets-Sheet 2 I nvenior:

Francis ar (4, M1 7/ A ril 3, 1934. F. w. DEAN UNIRETURN FLOW STEAM CYLINDER Filed Nov. 1, 1950 3 Sheets-Sheet 3 liq/entou- Frances Wliean 7 vuw7, fliiys.

il r Patented Apr. 3, 1934 UNITED STATES PATENT OFFICE 2 Claims.

This invention aims to provide a new and improved construction for cylinders and valves of reciprocating piston steam engines that have separate inlet and exhaust ports at each end of the cylinder. By means of this construction there is a movement of the incoming steam from the boiler as in uniflow engines, but with a return flow exhausting feature which improves its thermal action and thus its steam economy, and gives rise to the designation run-return flow engine.

The invention is illustrated as appliedto the two cylinder type of locomotive by drawings as delineated in Figures 1 to '7, although it is applicable to locomotives having any number of cylinders arranged in any way. The cylinder with its steam chest is shown as of cast metal in one piece, one cylinder being located on each side of the front end of the locomotive. The two cylinder castings extend toward each other, are bolted together under the middle of the smoke box of the boiler, and are curved on the upper central parts to fit the cylindrical smoke box to which they are bolted.

The cylinder is provided with a cast iron bushing for contact with the piston which slides within it, and the steam chest has two bushings within which the two valve pistons, composing the valve, move. The cylinder bushings are turned to tightly fit the accurately bored cylinder, and the ends of the bushing are faced off flush with the ends of the cylinder. The cylinder heads are in contact with both the cylinder and bushing ends, and the bushing is thus kept in place.

The steam chest has two cast iron bushings accurately fitting the bored chest, one being for each valve piston. Each steam chest bushing is stepped down in three places, as shown, and has faces which abut hard and steam tight against corresponding faces in the steam chest. The live steam pressure keeps the bushing in place as there is boiler pressure at the larger end and low back pressure at the smaller end. In addition there are tap bolts, not shown, passing through the steam chest shell and. penetrating the bushing.

The different figiu'es show elevations and sections which illustrate the assembly of parts, as follows:

Fig. 1 is a longitudinal section of the cylinder and steam chest with the piston, piston rod, valve, valve stem and other parts in place, from which their purposes can be discerned. In this figure the steam passes from the boiler to the steam chest through the cylinder heads.

Fig. 2 is a front end elevation of the cylinder and steam chest shown in Fig. 1.

Fig. 3 is a rear end elevation of the cylinder and steam chest shown in Figs. 1 and 2.

Fig. 4 is a vertical cross-section on a reduced scale taken on the dotted line 44 of Fig. 1, looking to the right.

Fig. 5 is a transverse section through the inlet port taken on the dotted line 55 of Fig. 1, looking to the right.

Fig. 6 is a section through the exhaust port taken on the dotted line 66, looking to the right.

Fig. 6a is a sectional detail of the exhaust openings through the cylinder bushing, shown in Figs. 1 and 6.

Fig. '7 is a longitudinal section through the steam chest, the upper part of the cylinder, and a passageway for the steam from the boiler directly to the ends of the steam chest instead of through the cylinder heads as shown in Fig. 1.

Fig. 8 is a section of a flattened steam pipe with strengthening cross ribs, for conveying boiler steam to the rear cylinder head when there is a driving wheel close to that head.

Nothing further will be stated concerning the means of passing steam through the cylinder heads.

The different parts are identified by numbers on the drawings as follows:

Numbers Designations of parts hea 3. .Figs. 1, 2, 3,4 Steam passages through the cylinder Figs. 2, 3

hea s.

a. Figs. 1,2, 3

Internal ribs in heads.

Live steam chambers in ends of steam chest.

Ball and socket joints between pipes 6,

10, and cylinder casting.

Steam chest bushings.

Valve pistons.

Pipes to convey steam from cylinder heads to the interior of the steam chest.

Figs. 1, 4, 7

. Fig. 1

Stufiing boxes in steam chest heads.

Live steam ports through steam chest bushings.

18. Figs. 1,5 Live steam ports surrounding steam chest bushings taking steam from 17 19. Figs. 1, 5 Steam passage from 18 to cylinder.

20 Figs. 1,6 Exhaust steam ports through steam chest bushing.

Numbers Designations of parts 21. Figs. 1, 6 Exhaust steam ports surrounding steam chest bushing, taking exhaust steam from 22 and delivering it through 20 to exhaust chamber 26.

22. Figs. 1, 6 Po21gtor2iveying exhaust steam from ports 0 l. 23. Figs. 1, 6, 6a Ports conveying exhaust steam from 2 Lugs to which crosshead guide bars are bolted.

Pipe conveying steam from boiler to both ends of steam chest.

The steam piston 25, Fig. l, is of the usual hollow type with flat faces and provided with packing rings. This piston moves back and forth an amount limited by the crank throw.

The valve of the uni-return flow locomotive is similar to that of the ordinary counterfiow locomotive, and is driven by any of the reversing Valve gears that are commonly applied to locomotives. The valve is of the piston type and consists of two pistons on one valve stem, one piston being located near each end of the steam chest. In the ordinary, or counterflow locomotive, one end of the valve piston for each end of the cylinder admits and cuts off the supply of steam to the port, and the other end of the same piston is sufficiently near the admission end to exhaust the steam through the same port, there being one port at each end of the cylinder, which serves both to admit and exhaust the steam.

In the case of the uni-return flow cylinder the valve motion is precisely the same as that of the counterfiow locomotive. As, however, in the unireturn flow engine, one end of each valve piston admits steam to and cuts it off from entering the inlet port and the other end exhausts it from another port, the valve'piston is longer than that of the counterflow locomotive in order to reach from one port to the other.

The economy of the unifiow engine is not due to all of its unifiow features, from which it derives its name, but to the facts that, firstly, the exhaust steam does not pass out through the inlet ports, and secondly, that the outward path of the steam from the vicinity of the cylinder heads is not parallel to those heads, but is inclined to them, and thus diminishes the sweeping of heat from the heads while exhausting occurs. The third feature of the conventional uniflow is that the exhaust steam in leaving the cylinder, sweeps over the ends of the piston and removes heat from them and somewhat nullifies the economy due to the first two features. The uni-return flow, engine, which is the subject of these specifications, retains the first two features of the conventional unifiow, but substitutes a superior one for the third, namely, that the exhaust steam flows directly away from the piston toward the other end of the cylinder. The name uni-return flow is derived from the features just described.

The conventional unifiow engine is not acceptable to railroads for locomotive use on account of its long and heavy cylinder and piston, the latter being so long that when it is at the end of its stroke one end is near the middle of the cylinder. The weight of the long piston is so great that it is diificult to counterbalance it by weights in the driving wheels. The long cylinder renders it necessary to spread the wheels of a four wheel forward truck and thereby to lengthen it and the whole locomotive. These additional lengths and consequent weights are objectionable.

The uni-return flow cylinder is practicable for locomotives because it is as short and nearly as light as that used on ordinary locomotives and can be substituted for them. There is an impor ant feature of the uni-return flow engine that is not possessed by the conventional unifiow, namely, that the piston of the latter on beginning its exhaust stroke immediately closes the exhaust port and thus compresses the steam remaining in the cylinder to so high a pressure that the engine is unfit for use if non-condensing, as in a locomotive, without a relief valve or large compression chamber. The piston of the uni-return flow engine, on the contrary, does not pass over and close the acting exhaust port, which is near the inlet end of the cylinder, until it is closely approaching that end. It thus does not create excessive compression.

Each valve piston is provided with the usual packing rings, two at each end for the purpose of making steam tight joints between it and the surrounding bushing, the piston itself being a loose fit in the bushing. Besides the end rings there is one in the middle, the object of which is to prevent exhaust steam from passing out through the inlet port and around the loose fitting piston to the exhaust port and thence to the exhaust chamber whenever the design is such that the two exhaust rings are within the exhaust port width, and the inner inlet ring is within the width of the inlet port at the same time. The passage of exhaust steam through the inlet port violates a fundamental principle of the unifiow engine, which is that the exhaust steam should pass out only through a special exhaust port.

The operation of the engine is as follows: Steam flows from the boiler to the steam chest through pipes, not shown, in the usual manner, indicated by 4 on Figs. 1, 2, 3 and 4, and by 34 on Fig. 7.

Fig. '7 shows the valve in the central position in which case both inlet ports are closed by the lap of the valve, the lap being the amount which the valve extends beyond the inlet port at each end of the steam chest. The exhaust ports may be closed by the exhaust lap of the valve at each end, or just ready to open if the exhaust lapis O, or slightly open if the valve has exhaust negative lap, or so-called clearance.

Fig. 1 shows the valve at or near its extreme travel to the right, in which case the left inlet ports 1'? through the bushing are open, steam being thus admitted to the surrounding spaces 18 and 19, Figs. 1 and 5, and forcing the piston 25 to the right. In this position of the valve the right exhaust ports 20, Fig. 1, are open to permit the exhaust steam on the right of the piston to pass out through the ports 23, 22, surrounding space 21 and ports 20 to the exhaust chamber 26, shown in Figs. 1, 'l and 6, from which it proceeds laterally to the smoke stack.

When the cylinder piston has nearly reached the end of its travel to the right. the valve has already moved back to the left and closed the left inlet ports 17 and connecting spaces. At this 150 time the left end of the right valve piston closes the right exhaust ports 20, Figs. 1 and 6, and compression by the cylinder piston occurs. At about the same time the cylinder piston passes over and closes the circular ports 23 and produces additional compression in a smaller volume. When the valve travel is reduced by moving the reverse lever the cut-off occurs earlier, the valve will close the exhaust ports 20 earlier and compression begins before the piston closes the ports 23, but at late cut-offs this is reversed.

When the cylinder piston is approaching the end of its stroke at the right, the valve will be moving to the left and will open the right inlet ports 17. On the arrival of the piston at the end of its stroke this port will be open by an amount known as its lead. At this time the left valve piston will have uncovered the left exhaust ports 20 and the steam on the left side of the cylinder piston will pass out through the left ports 23, 22 and 20 to the exhaust chamber 26 and thence to the smoke stack.

On approaching the end of its stroke in either direction the cylinder piston passes over and beyond the exhaust holes or ports 23 and allows the steam on its active or propelling side, which is now at low pressure, to pass through these holes into the connecting spaces, but as the valve has closed the ports 20, it can go no farther. The removal of some steam from the cylinder at this time into this closed space, slightly anticipates the exhaust which is about to take place through the holes 23 at the opposite end. of the cylinder, and is slightly advantageous in reducing back pressure. The phenomena described occur alternately at one end and the other of the cylinder as the locomotive operates.

Locomotives with piston valves are now designed with the valve stems outside of a vertical line through the centers of the piston rods instead of directly over them, in order to simplify the connections between the valve gears and valve stems. It is important to preserve. this feature in the uni-return flow engine, but on account of the sensitiveness of the pistons to side pressure, as the pistons are always smaller in diameter than the cylinder and easily move transversely, means of preventing this pressure must be provided, as experience shows that it causes serious pounding by the pistons against the sides of the cylinder when the pistons pass over the holes or ports in the cylinder bushings. The lateral movement of the pistons will occur (see Fig. 6) whenever the exhaust steam can pass directly from the cylinders to the valve on an incline. Which incline is caused by the side offset of the steam chest.

In my present construction I accomplish this in part by distributing the port holes 23, Figs. 1 and 6, symmetrically with respect to a vertical line through the center of the steam cylinder, and further by providing a dividing rib 28, Fig. 6.

This rib is placed with the center of its lower end directly over the center of the cylinder and in contact with the bushing. After extending vertically a short distance, the rib curves, proceeds straight towards the center of the steam chest bushing, and terminates in contact with it. Its function is completed by a short rib 28a, Fig. 6, which also is directed towards the center of the bushing and is in contact with it. Still further the ports in the steam chest are the same in number and size on each side of the dividing ribs. By these means the exhaust steam in escaping from the cylinder is compelled to move vertically until after it leaves the cylinder, and it cannot, therefore, exert horizontal pressure on the piston and produce pounding.

On opposite sides of the dividing rib 28 there are ribs 29 for tying together the walls of the exhaust ports 22, Fig. 1, which are placed in positions for strength and minimum obstruction to the how of steam.

In Fig. 5, a straightening rib 30 is shown tying together the walls of the inlet ports 19, Fig. 1.

I claim:

1. The combination with a uni-return flow steam cylinder of a steam chest containing inlet and exhaust ports at each end, and a valve piston and bushing therefor at each end of the steam chest and means to reciprocate the valve pistons in unison, each valve piston having a plurality of packing rings at the inlet end to prevent leakage of steam into the inlet port when it is closed, or into the exhaust port when the inlet port is open, and a plurality of rings at the opposite end of the same valve piston to prevent leakage of steam from the exhaust port to the exhaust chamber, and an intermediate ring in each valve piston to prevent steam in a certain position of the valve from exhausting through the inlet port and around the outside of the valve piston between it and the bushing, to the exhaust chamber.

2. The combination with a uni-return flow steam cylinder and its piston, of a steam chest offset therefrom, exhaust passages leading from the steam cylinder through a series of ports equal in number, area and shape symmetrically arranged with respect to a vertical center line of the cylinder, and a partition rib extending from the vertical center line of the cylinder at the outside of its bushing at its top, curved and directed to the center of the steam chest bushing, a short rib from a point near the top of the steam chest bushing opposite the upper end of the partition rib and directed to the center of the steam chest bushing, and ports through the chest bushing equal in number and size on each side of the partition ribs to prevent lateral movement and pounding of the cylinder piston against the cylinder walls.

FRANCIS W. DEAN. 

